Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 231907
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
307 PM EDT Thu Mar 23 2017

.SYNOPSIS...
High pressure ridged across the lower Great Lakes will continue fair
weather through late evening. A warm front will then bring a period
of rain to western New York with some mixed wintry precipitation
from the western Finger Lakes eastward late tonight and Friday.
Expect much warmer temperatures on Friday behind the front. The
front will stall across the region this weekend, with several
disturbances moving along the front and bringing periods of rain
over the weekend and into the first half of next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
High pressure ridging across New York will continue to shift its
center over the mid Atlantic states through this afternoon resulting
in the present fair weather and sunny skies. High clouds are
approaching from the west in advance of our next system.
Temperatures will warm to around 40 across far Western New York with
lower to mid 30s elsewhere.

Surface ridging will keep us dry through much of tonight with mainly
increasing and lowering clouds. Temperatures will bottom out around
midnight in the low 30s across western New York with 20s across
central New York. After midnight, increasing southerly flow will
help temperatures begin a slow climb ahead of a warm front lifting
across the Ohio Valley. Models show an axis of 925-700mb moisture
being lifted ahead of the warm front and on the nose of a 40-50kt
jet. Precipitation will begin to overspread western NY between 09-12z
where surface temperatures will be very critical on p-type at the
ground. Using a warm layer tool which produces a p-type based on a
warm layer aloft and looking at surface temperatures, have included
some freezing rain across the extreme interior southern Tier into the
western Finger Lakes for a few hours before changing quickly over to
plain rain as surface temps rise above freezing. Have issued a
Winter Weather Advisory to cover the areas most likely to see a
trace to a tenth of an inch of ice. There may be some sleet too but
the more dominant p-type will be freezing rain. This idea matches
very well to ensemble guidance from the SSEO/NCAR/SREF. All other
areas of western NY appear to have surface temps above freezing when
the rain arrives including Jamestown to Buffalo to Rochester. Total
liquid QPF will run around a quarter of an inch.

As the warm front approaches then crosses western NY on Friday,
expect precipitation to begin to overspread the eastern Lake Ontario
region around Sunrise where temperature profiles support some Snow
changing to sleet and freezing rain before switching to plain rain
around Noon. Up to two inches of snow are possible here along with
up to a tenth of an inch of ice which also lead to a Winter Weather
Advisory. Total liquid QPF after the mixed precip here will also
run around a quarter of an inch.

As the warm front shifts across western NY, expect rain to
taper off to a chance of some more spotty showers by noon with a
possibility that much of the region south of the front may in
fact see drying with some breaks of sun through the afternoon.
Temperatures will warm nicely into the 50s across western NY
behind the front with 40s for Highs east of Lake Ontario where
the front may stall leaving rain in the forecast through the
day.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...

By Saturday night a sharp frontal boundary will be in place across
the Great Lakes from southern WI to northern New England as broad
southerly return flow around high pressure stationed off the Eastern
Seaboard and a large, vertically stacked low over the southern
Plains encounters an anticyclonic flow of cold and dry air moving
down from the north out of Canada. A broad swath of precipitation
will be in place along this front Friday night thanks to
aforementioned convergence and frontogenetic forcing along and north
of the boundary. Latest model consensus places the axis of this
precipitation primarily north of the Thruway, with the bulk of the
precip falling across Ontario and the North Country. Precip type
should remain all rain, as virtually all of the forecast area should
stay on the warm side of the frontal boundary, with lows ranging
from near 50 along the PA border to the mid 30s in the St. Lawrence
valley.

The frontal boundary will shift south across the forecast area on
Saturday as the high over Canada shifts position eastward across
James Bay. A low-level northeasterly flow of colder air will ooze
back into the forecast area from the northeast during the
day...depressing temperatures across the area, with highs barely
budging from overnight readings. Temps should only top out in the
mid 50s along the PA border, with low 40s across the Buffalo-
Rochester metros, and upper 30s in the St. Lawrence valley. Precip
should taper off in intensity/coverage as we move through Saturday,
as upper level forcing diminishes with the departure of an upper
level jet max over eastern Ontario/Quebec.

The arrival of shallow cooler air from the northeast will once again
present precip type issues Saturday night into Sunday morning, as
temperatures fall below freezing across the North Country, bringing
back a potential for freezing rain from the Tug Hill north to the
St. Lawrence River. Precip should stay as rain elsewhere though, as
temperatures should range from the mid 40s along the PA border to
the mid 30s along Lake Ontario. With upper level ridging amplifying
across the area, precipitation should taper off to showers
overnight, before precipitation ramps up again Sunday into Sunday
night, as the upper level low that will be drifting across the
Midwest during the first half of the weekend approaches the Great
Lakes. Strengthening southerly flow with the approach of this
feature and its attendant surface low will shove the cold front back
to the north, with highs running from the 50s in Western NY to the
low 40s in the North Country. Lows Sunday night will run in the 40s,
meaning that precip should once again fall entirely as rain.

Regarding flooding concerns, while warming temperatures will
accelerate melting of remaining snowpack across the forecast area,
the axis of heaviest rainfall Friday night should fall primarily
across Canada. There will be enough of a break in the steady
rainfall Saturday/Saturday night to allow for some recovery in
stream levels before the next round of rain arrives Sunday.  All
told, current MMEFS hydro ensemble guidance suggest that area
streams may rise to action stage, but no flooding is currently
expected.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
An active wet pattern will continue Sunday into at least the middle
of next week as western and north-central NY will remain within the
track of at least two mid-level troughs. Each of these troughs will
provide synoptic lift over and moist southerly flow into our region
that will interact with a low frontal boundary. The first will shift
over our region in the Sunday-Monday time frame while the second
looks to shift over our region Tuesday. It appears now that this
boundary from Sunday into Monday will lie further to the north
towards or across the Saint Lawrence River Valley then should be
shoved even further northeast by the second trough/surface low. For
western NY into the Finger Lakes, the position of this front will
allow for plenty of low level warm air to support high confidence
for a soaking plain rain. Looking across the North Country into the
Saint Lawrence Valley, the position of the front will be more
sensitive to p-type and a risk for some freezing rain Sunday night
and Monday night with cold northeasterly flow down the SLV. Have
kept any wording for freezing rain at chance POPs due to the
uncertainty in frontal position this far out.

In terms of surface temperatures, areas to the south of the front
will mainly feature warmer temps upper 40s into the 50s while areas
north of the boundary will see cooler temperatures 30s and lower 40s
with some 20s possible in the North Country during the overnights.

In terms of QPF, a rough average accumulated total among the models
Sunday through Tuesday ranges from around a half inch on the ECMWF
to around 2 inches on the GFS. While the long duration of this event
should not bring any flash flooding concerns, river and stream rises
and areal flooding of low-lying areas may be possible. If sub-
freezing air remains locked at the surface on the north side of the
front there could also be a threat of some significant ice
accumulations but the lowest confidence is found in that scenario.
Overall, confidence on the specific placement of any weather hazards
during this period is fairly low at this range which has precluded a
mention in the Hazardous Weather Outlook.

On Wednesday, the second surface low will shift off into New England
with a cooler and perhaps very dry northwest flow in its wake. The
12z ECMWF shows very dry air with just a cool northwest flow on
Wednesday while the GFS shows some lingering wrap around moisture
may lead to some upslope/lake enhanced showers. Have gone with
slight/low chance POPS for Wednesday under a more clear signal shows
up in the guidance.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
High pressure ridged across the region will continue dry/fair
weather through late this evening with increasing and lowering
VFR clouds.

A warm front will lift across the Ohio Valley tonight with rain
overspreading western then central NY. All TAF sites in WNY should
see plain rain beginning 09-11z but some interior airfields toward
the western Finger Lakes could see some light freezing rain at the
start before changing over to rain. This will also bring in MVFR
cigs.

The front will lift across western NY through the morning on Friday
with KART seeing some SN/PL/FZRA with IFR VIS and MVFR cigs around
12z before changing over to plain rain by around 15z. There also
looks to be a risk for LLWS Friday morning across WNY as a 40-50
knot low level jet arrives. Some IFR cigs could arrive at KJHW/KART
Friday afternoon.

Outlook...

Friday night through Tuesday...MVFR/IFR cigs with rain likely at
times.

&&

.MARINE...
High pressure ridged across the lower Great Lakes will maintain
light winds and negligible waves through late this evening.

South to Southwest winds will increase Friday as a warm front lifts
into the eastern Great Lakes. Winds will approach small craft
criteria across eastern portions of Lake Erie and Ontario but waves
look to remain below 4 feet. After this, a warm frontal boundary
will stall across the region, with a northeasterly flow likely on
Lake Ontario and variable winds on Lake Erie. This may require small
craft headlines on Lake Ontario at times this weekend.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory from 6 AM to noon EDT Friday for
     NYZ006>008.
     Winter Weather Advisory from 5 AM to 11 AM EDT Friday for
     NYZ004-005-013-014-021.
MARINE...None.

&&

$$

SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...WOOD
LONG TERM...SMITH
AVIATION...SMITH
MARINE...SMITH


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